JP5430810B2 - Electron impact active pixel sensor - Google Patents

Description

Field of the Invention The present invention relates to an apparatus for imaging or detecting useful images at low light quantity using an active pixel sensor in an electron impact mode that uses a photocathode for detecting and imaging at low light quantity. And methods.

BACKGROUND OF THE INVENTION Many important applications have been made in various fields for cameras that operate with low light intensity. This includes photography, night vision, surveillance, and scientific use. Modern night vision systems, for example, are rapidly changing from direct vision systems to devices using cameras. These are being accelerated by continuous advances in video display and processing. Video-based systems allow remote display and can be merged with other images, such as from a forward-looking infrared sensor, to allow viewing, recording, and image processing. Surveillance applications are also becoming more prevalent with video, but in this example camera size, performance and low light sensitivity are often problematic. Scientific applications require cameras with good photon sensitivity over a wide spectral range and high frame rate. In these applications, there is a greater need for an improved low light sensor that can output video directly.

Image sensing devices incorporating image sensor arrays are commonly used in electronic cameras. Each pixel generates an output signal in response to incident light. The signal is typically read one row at a time to form an image. Prior art cameras used a charge coupled device (CCD) as an image sensor. To increase the sensitivity, the image sensor incorporating the amplifier Kakue element is known as an active pixel sensor (also referred to as APS). Active pixel sensors are described, for example, by Merrill, US Pat. No. 5,789,774 issued Aug. 4, 1998, by Dickinson et al., US Pat. No. 5,631,704 issued May 20, 1996, Tomura et al., US Patent No. 5,521,639 issued on May 28, 1996, Merrill, US Patent No. 5,721,425 issued on February 24, 1998, Lee et al., US issued April 29, 1997 No. 5,625,210, Merrill, US Pat. No. 5,614,744 issued Mar. 25, 1997, and Ackland et al., US Pat. No. 5,739,562, issued Apr. 14, 1998. In a related field of active pixel sensors, there is a paper by Fossum "CMOS image sensor: electronic camera on one chip", IEEE Transactions on Electron Devices, Vol. 44, No. 10, pp. 1689–1698 (1997). This paper is incorporated herein by reference.

  In general, it is desirable to provide a camera that produces high quality images over a wide range of light levels, including extremely low light levels, such as in the case of starlight and lower illumination levels. In addition, the camera should be physically small in size and have a gentle electronic power requirement, so that it can be carried, mounted on the head, and operated with other batteries. It can be. The active pixel sensor camera meets the requirements for miniaturization and low power, but the sensitivity is low at low light, and its performance is limited to 0.1 lux or high light conditions.

  Conventionally, night vision cameras that operate under extremely low light levels are known. Standard low light cameras in use today are third generation (GaAs photocathodes) or second generation (multi-alkali photocathodes) optically coupled to CCDs to form image enhanced CCD or ICCD cameras. ) Based on image intensifier tube fiber. The scene to be imaged is focused on the photocathode faceplate assembly by the input lens. Incident light energy releases photoelectrons from the photocathode to an electronic image, forming an electronic image. The electronic image is focused near the input of a microchannel plate (MCP) electronic multiplier, which enhances the electronic image by secondary amplification while maintaining the geometric integrity of the image . The enhanced electronic image is focused near a fluorescent screen, which converts the electronic image into a visible image (typically visible through a fiber optic output window). A fiber optic taper or transfer lens then transmits this amplified visual image to a standard CCD sensor, which converts the light image into electrons that form a video signal. In these existing prior art ICCD cameras, there are five interfaces through which images are sampled, each of which reduces the resolution and adds noise to the signal of the ICCD camera. This image degradation, which could not be avoided before, is a serious drawback for systems that require high quality output. ICCD sensors are also large and heavy due to the molten fiber optic. A third generation MCP image intensifier is described, for example, in US Pat. No. 5,373,320 issued Dec. 13, 1994 to Johnson et al. The camera attachment described in this patent converts a standard daylight video camera into a day / night camera.

  In addition to image degradation resulting from the multiple optical interfaces of an ICCD camera, it is even more problematic that the MCP is a relatively noisy amplifier. This added noise in gain processing further degrades the image quality of low light quantities. The noise characteristics of MCP are characterized by an excessive noise factor Kf. Kf is defined as the signal-to-noise power ratio at the MCP input divided by the signal-to-noise power ratio at the amplified MCP output. This Kf is a measure of the degradation of the signal-to-noise ratio for MCP gain processing. A typical value for Kf is 4.0 for third generation image intensifiers. A low noise, high gain MCP for use in a third generation image intensifier is disclosed in US Pat. No. 5,268,612 issued Dec. 7, 1993 by Aebi et al.

  Another gain mechanism is achieved by electron impact semiconductor (also referred to as EBS) gain processing. In this gain processing, gain is achieved by electronic amplification that occurs when a high-speed electron beam disperses its energy in a semiconductor. Dispersed energy creates electron-hole pairs. For semiconductor silicon, one electron-hole pair is generated for each incident energy of approximately 3.6 electron volts (eV). This is a very low noise gain process with a Kf value close to 1. A Kf of 1 indicates gain processing to which noise is not added.

  Electron impact semiconductor gain processing is disclosed in US Pat. No. 5,347,826 issued Dec. 20, 1994 by LaRue et al. And US Pat. No. 5,475,227 issued Dec. 12, 1995 by LaRue et al. As shown, it was used in a focused electron impact hybrid photomultiplier tube consisting of a collection of anodes consisting of a semiconductor diode placed in a photocathode, a focus electrode and a detector. The disclosed hybrid photomultiplier tube is very sensitive but does not detect images.

  Electron impact semiconductor gain processing has been used to affect image degradation in ICCD low light cameras. A backlit CCD is used as an anode that is almost in focus with the photocathode to form an electron impact CCD (EBCCD). Photoelectrons from the photocathode are accelerated and imaged directly on the backlit CCD. Gain is achieved by low noise electron impact semiconductor gain processing. EBCCD eliminates the MCP, fluorescent screen, and fiber optics, resulting in improved image quality and increased sensitivity in smaller cameras. Remarkable improvement of degraded resolution and high noise due to conventional image transfer chain was realized by EBCCD. EBCCD is disclosed in US Pat. No. 4,687,922 issued August 18, 1987 by Lemonier. The background of EBCCD is Ebi et al.'S paper "Gallium Arsenic Electron Impact CCD Technology" SPIE, Volume 3434, pp. 37-44 (1998), which is also incorporated herein by reference.

  A special CCD is required for optimal low-light EBCCD performance. The CCD is required to be thin at the rear to allow high electron impact semiconductor gain. CCDs cannot be used in the front impact mode used in standard CCD cameras when the gate structure prevents photoelectrons from reaching the semiconductor and low electron impact semiconductor gain is obtained at moderate acceleration voltages. The high acceleration voltage required to penetrate the gate structure damages the CCD and shortens the life of the CCD. A frame transfer format is also required if the CCD has both an image area and a storage area on the chip. The image and storage area are approximately the same size. The frame transmission format is required for two reasons. First, the CCD image area has a high filling factor (minimum dead area) if possible. The frame transfer CCD architecture satisfies this condition. The line voltage architecture provides a substantial dead area (on the order of 70-80%). The reduction of the active area causes the photoelectrons to be lost. This means a decrease in photoelectron cathode quantization efficiency or sensitivity. At the lowest light level (starlight or cloudy starlight), the performance of a low light camera is represented by photon statistics. For sufficiently low light resolution and performance, it is essential that the maximum number of photons be detected by an imager. Secondly, due to the frame transfer format, signal integration can occur during the storage area reading in addition to the integration period. This allows charge to be accumulated with the collected signal substantially continuously maximized.

  EBCCD cameras have further disadvantages. Frame transition CCD architecture has a difficult problem for the EBCCD example where the required vacuum envelope size needs to be doubled due to image and storage requirements on the CCD. This condition also means that the frame transfer CCD chip will double the size of the image area. This substantially increases the cost of CCE for inter-row transfer CCDs or active pixel sensor chips, where the chip cannot be manufactured on a silicon wafer basis. EBCCD-based cameras also have the disadvantages of CCD back lighting that require special processing to thin the semiconductor and passivate the rear surface for high electron impact semiconductor gain. This process is not standard in the silicon industry and substantially increases EBCCD manufacturing costs. EBCCD cameras consume several watts of power due to CCD clock conditions and require external electronics for the entire camera. The size of the external camera electronics hinders applications that have the advantage of manufacturing the camera. Finally, CCDs require special semiconductor production lines that are not compatible with major CMOS semiconductor manufacturing technologies. This further increases the cost of cameras using CCD.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate various drawbacks of the prior art and provide an improved low light image system and corresponding method. This is achieved by using an active pixel sensor CMOS imager in electron impact mode in a vacuum envelope with a photocathode sensor. The electronic impact active pixel sensor consists of a low light camera with a lens, housing, power and control interface.

  Another object of the present invention is to describe an improved low light camera that utilizes an active pixel sensor CMOS imager and direct electron impact.

  In addition, it is an object of the present invention to provide an improved apparatus for various low light imaging applications that significantly eases the power requirements to facilitate the formation of a lightweight structure in which the image circuit is used. To describe a new chip or image circuit that can be provided.

  Further features and embodiments of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION An active pixel sensor chip is shown in FIG. The architecture of the light gate active pixel sensor is shown in FIG. 2 and is that of the photodiode active pixel sensor of FIG.

  In FIG. 1, a pixel array 11 controlled by logic timing and control circuit 12 is shown. The signal is processed by a signal processor including an analog processor and an analog-to-digital converter. The column selection control circuit is indicated by reference numeral 15 and the output signal is shown to be provided from the active pixel sensor as indicated by arrow 16. The output at arrow 16 may consist of a digital or analog signal depending on the system in which the active pixel sensor is used or the signal is supplied.

  Two basic pixel architectures are used to form the individual pixels of the pixel array 11. The first architecture for the pixel is a light gate pixel configuration. The architecture for the second pixel is a photodiode pixel configuration.

  In FIG. 2, an optical gate type pixel configuration is shown. The photoelectrons generated by the incident photon flux are collected under the optical gate 74. The optical gate (similar to a gate formed on a CCD) has a polysilicon electrode on a dielectric layer over the charge storage region. The optical gate is biased by a power supply applied at 67. The optical gate is separated from the floating output diffusion mode 72 by a transmission gate 75 and a bridge diffusion 73. The transmission gate is biased by the power supply applied at 66. The potential wells generated by these applied bias potentials in the semiconductor are indicated by broken lines, but charges are accumulated below the optical gate by the applied bias potential. For reading, the floating output diffusion electrode is reset by the voltage applied as indicated by reference numeral 61 (also referred to as the drain voltage), but this voltage application was normally turned off. This is when the gate 62 of the reset transistor 64 receives a power pulse to turn on the transistor and set the floating output diffusion to the drain voltage. The photogate voltage is instantaneously pulsated to transfer the collected charge to the floating output diffusion electrode 72. The charge that generated the light is detected when the row selection transistor 63 is turned on by applying a voltage pulse to the transistor 69. The charge is amplified by the source follower transistor 59, and the voltage is detected by an analog signal processing circuit (see FIG. 1) connected to the column bus 65. The optical gate configuration (FIG. 2) (comparable to the photodiode pixel configuration shown in FIG. 3) has the advantage of low read noise because the measured voltage by the source follower transistor is reset. This is because the associated double sampling readout can be integrated into the pixel when the difference between the signal level and the signal level, but due to the light absorption into the intervening polysilicon layer, the optical sensitivity is low. It has the disadvantage of being low.

  In FIG. 3, a photodiode type pixel configuration is shown. Photoelectrons generated by the incident photon flux are applied when the reset transistor 24, which is normally off, receives a pulse signal from the power supply to turn on the transistor and set the photodiode bias to the drain voltage. Collected on a reverse-biased photodiode 20 by a power supply applied as indicated by reference numeral 21 (also referred to as the drain voltage). The photogenerated charge is detected when the row selection transistor 23 is turned on by applying a voltage pulse to the transistor gate 29. The electric charge is amplified by the source follower transistor 19, and the voltage is detected by the analog signal processing circuit 13 (see FIG. 1) connected to the column bus 25.

Cameras with active pixel sensors have significant advantages over cameras with charge-coupled devices. These advantages include a substantially advanced electronic integration, power requirements, where most of the required camera electronics are integrated on the APS chip where the electronics include integrated timing and control electronics. significant relaxation, the use of low cost standard CMOS fabrication technology, overall reduction in volume of the camera, and a variable of a certain image reading. Image readout modes can include window readout of sub-regions of the entire array or skip readout where pixels are read every nth (n is an integer). In both of these modes, a portion of the pixel is read out allowing a high frame rate.

In FIG. 4, an electron impact active pixel sensor vacuum system or tube 33 according to the present invention is shown. This system consists of a photocathode 31, preferably a semiconductor photocathode such as GaAs or InP / InGaAs transfer electron photocathode for high performance applications (this includes a special active pixel sensor chip 32 that forms the electrode of the tube). May be included). The photoelectrons 35 are emitted from the photocathode 31 in response to the incident light indicated by the arrow 36. These electrons are accelerated by the applied voltage to an energy that is captured by the active pixel sensor 32 and is sufficient to allow electronic gain in the chip. This allows the chip to be biased near ground potential that allows easy interfacing with other elements. A control signal and bias voltage 38 may be applied to the active pixel sensor 32 and the video output signal 40 may be retrieved from the sensor 32. The base of the tube 33 in FIG. 4 is a transparent face plate, and the side wall 39 of the tube extends between the transparent face plate where the photocathode 31 is located and the header assembly 34 (where the APS chip is located). The header assembly 34 also provides an electrical feedthrough for applying a voltage 38 to the APS chip and a means for the video output signal 40 from the APS chip.

  The electronic shock sensor gain is preferably high enough to overcome the read noise. As a result, one photoelectron can be detected.

  The active pixel sensor for this application is modified for electron sensitivity using an electron impact semiconductor mechanism. A preferred embodiment is to eliminate conditions such as thinning and passivating the rear surface of the active animation layer sensor chip in surface electron impact mode. The surface electron impact approach makes the elements of an electron impact active pixel sensor the lowest cost. However, it is important that the low light performance is not significantly degraded by this approach. This is because the photodiode occupies a significant proportion of the pixel area in order to enable a high filling factor. A fill factor greater than 50% is desirable for good low light performance. A 50% fill factor results in low noise sensitivity for electron impact active pixel sensors comparable to an image intensifier tube CCD system using a third generation image intensifier tube.

  An electron impact active pixel sensor element incorporating a surface electron impact pixel sensor chip preferably uses a photodiode active pixel architecture. This is because all the overlying material can be transferred to the surface of the photodiode semiconductor in this pixel arrangement. The material intervening between the semiconductor and the incident electrons can absorb the electrons, provide a low electron impact semiconductor gain, and disperse the electron energy that requires a high acceleration voltage. The photogate active pixel sensor architecture has the disadvantage of requiring overlying polysilicon or other material that prevents the collection of incident photoelectrons for typical acceleration energy (2 keV). Incident electrons also cause radiation loss to the dielectric, and the silicon interface provides a short operating lifetime for the surface electron impact light gate active pixel sensor chip.

  The photodiode should have a high electron impact semiconductor gain at a relatively low electron acceleration voltage (preferably 2,000 volts or less). This minimizes the radiation loss to the CMOS imager due to x-rays generated by electron impact on the active pixel sensor chip on silicon or components located above it. Low voltage operation is also desirable to allow easy gate operation in the booster tube by controlling the applied voltage. In addition, it is desirable to protect adjacent CMOS circuits from electron impact by providing an overlying protective layer with conductivity that releases charge accumulation and prevents damage by electrostatic discharge. Protection also reduces X-ray exposure to the underlying CMOS circuit.

High electron impact semiconductor gain at low electron accelerating voltages can be achieved by removing the overlying layer from the photodiode surface and minimizing the semiconductor surface to minimize carrier recombination at the surface. Dynamics are needed. This passivation can be achieved by many techniques known from the prior art. One standard technique is to form a lightly doped region on the semiconductor surface. The thickness of this doped region should be equal to or less than the electronic range in the solid, preferably substantially smaller, at the desired operating voltage. For operation at 2,000 volts, the electron string is about 600 angstroms of silicon. The approximate electron string in the solid is given by the Gruen string, R _G , where R _G = 400 _{E b} ^1.75 / ρ. R _G is angstroms, E _b is keV, [rho is gm / cm ³ units. In the case of silicon, the bulk density, ρ, is 2.33 g / cm ³ .

The doped region is doped to have the same carrier type with a higher free carrier concentration than the underlying region. The increase in doping density creates a potential barrier that prevents the desired small number of carriers from recombining and arriving at a surface that is not collected by the reverse-biased photodiode. Other techniques for forming a potential barrier are known in the art to prevent a small number of carriers from reaching the surface. Passivation techniques are disclosed in US Pat. No. 4,822,748 issued Jan. 18, 1989 by Janesik et al. And US Pat. No. 4,760,031 issued Jan. 26, 1988 by Janesik.

  Another embodiment of the present invention utilizes a rear impact active pixel sensor chip. In this embodiment, the APS chip is placed face down and the silicon substrate is mechanically and chemically removed leaving the thinned active pixel sensor chip.

  A method for thinning a substrate associated with a CCD is disclosed in US Pat. No. 4,687,922. This disclosed method can be used to thin the back side of APS components and is hereby incorporated by reference. In general, thinning the back surface can be accomplished by thinning the substrate under the sensitive area.

  A cross section of the photodiode pixel structure before thinning the substrate is shown in FIG. The photodiode 20 of FIG. 3 is shown as region 55 in FIG. Included in region 53 is a CMOS circuit consisting of associated transistors (transistors 19, 22, and 23 in FIG. 3) in the pixel. First, a rapid isotropic etching process is performed to remove most of the substrate 51. For example, when the substrate is initially about 400 μm, this etching process continues until about 380 μm of the substrate layer 51 is etched leaving a thin layer of about 20 μm of substrate material. This etching process is performed using a solution of nitric acid, acetic acid, and hydrofluoric acid in a ratio of 5: 3: 3, or a conventionally known solution. By rotating the substrate during this etching, a final thickness with good consistency is formed. A slow etch is then performed to remove the remaining substrate material and the etch is stopped at layer 57. This etching is carried out with an acidic solution in the presence of hydrogen peroxide at a rate of 5 ml per 350 ml or a similar solution of the prior art with a ratio of 3: 8: 1 nitric acid, acetic acid and hydrofluoric acid. The doping difference between layers 57 and 51 is used to obtain etch sensitivity. Etching is performed to ensure that the thickness has good uniformity. After thinning the active pixel sensor, the rear surface is passivated to reduce the surface recombination rate and ensure high electron impact gain at low operating voltages (<2 kV).

  Substrate removal and backside passivation ensure that photons and photoelectrons are absorbed sufficiently close to the potential source, and in this example, the charge collection achieved with a reverse-biased photodiode is generated. The charged charge can be made to reach the destination without bulk or surface recombination or lateral diffusion.

  In the exposure mode, electrons from the photocathode are incident on the rear surface of the chip as in the case of EBCCD described above. This approach requires additional processing for the attachment and thinning of the APS chip, but since there are no intervening structures on the electron impact surface, a 100% fill factor is obtained and the incident photoelectrons All have the advantage that potentially all can be eliminated by creating a suitable electrostatic potential distribution in the solid by manipulating the doping profile in a manner known as prior art. Thinning the backside exposure and backside is compatible with either photodiodes or photogate pixel structures. The potential distribution in layer 57 can be formed to deflect the generated electrons away from the CMOS circuit to a photodiode or photogate structure. This enables excellent low light sensitivity.

  Although not preferred, another embodiment of the present invention utilizes a front impact active pixel sensor chip coated with an electro-optic conversion layer. This is explained in connection with FIG.

  This approach has the advantage of using an unmodified standard chip for direct electronic sensitivity. This type of active pixel sensor is shown in FIG. In FIG. 6, a cross section of an active sensor with a front electro-optical conversion layer is shown. A photodiode (reference numeral 20 in FIG. 3) or a photogate (74 in FIG. 2) is shown as region 85 in FIG. Region 83 includes a CMOS circuit consisting of associated transistors or gates (transistors 19, 22, and 23 in FIG. 3) or transistors and gates 75, 64, 63, and 59 in FIG. These components are included in the substrate 81. An optical protective layer 86 is used to prevent light generated by the electron-to-light conversion layer 84 from entering the region 83. Aluminum so that the generated light can be reflected back to the light conversion layer (where reflection occurs in the region 85 where the light arrives, where it is detected by a photodiode or photogate structure). Or layer 86 is made of other highly reflective metals. The light conversion layer 84 is coated with an electrically conductive layer 82 that is optically reflective. Layer 82 forms a conductive electrode layer for the electron impact active pixel sensor to collect incident electrons and discharge them to a bias power source. Layer 82 also prevents light generated in layer 84 from reaching the photocathode. When light from this layer arrives at the photocathode, optical feedback is provided and excessive noise is added to the sensed image. Typically, layer 82 attenuates the light coming from layer 84 to the photocathode by at least three orders of magnitude to minimize optical feedback effects.

  In this embodiment, a standard active pixel sensor chip can be used with the electro-optical conversion layer and associated structure application shown in FIG. Electrons accelerated from the cathode to the anode are converted into photons by the conversion layer and detected by the APS pixel. This screen is deposited directly on the active pixel sensor chip. In this approach, layer 82 is fabricated using aluminum with relatively low incident electron energy and good optical reflectivity and good electron transmission properties. Optical reflectivity is important to allow more of the generated light to reach the photogate or photodiode for higher sensitivity. In this case, light striking the layer 82 is reflected back to the pixels and detected, increasing screen efficiency. Layer 84 is fabricated using a high efficiency phosphor such as P20 or P43 (emitting in green). It is further optimized by selecting a phosphor that emits light having a wavelength that matches the peak sensitivity wavelength of the active pixel sensor. The conversion layer may consist of a standard metallized phosphor screen of the type known in the prior art.

  The disadvantage of the approach using a conversion layer on the surface is that the active pixel sensor chip results in lower resolution and higher noise compared to direct detection of electrons. The reduction in resolution results from light scattering in the light conversion layer that results in pixel-to-pixel crosstalk and reduces the modulation transfer function. Higher noise results from excessive noise factor reduction due to an additional conversion process integrated with the light conversion screen. Higher noise also arises from the fact that the electron acceleration voltage needs to be substantially higher to achieve a good conversion gain. This is due to inefficiencies in the light conversion layer that typically require voltages higher than 4 kV for good conversion efficiency. High acceleration voltage significantly increases the X-ray generation rate. X-rays detected by the photocathode result in large noise pulses. X-rays also drastically shorten the lifetime of active pixel sensor chips due to radiation loss effects. Optimizing the light conversion components for maximum efficiency and enabling low voltage operation using the techniques described above can reduce noise effects.

  In FIG. 7, a camera according to the present invention is shown to illustrate various imaging systems. In this figure, reference numeral 140 indicates an image focused on the photocathode 142 via the lens 141. A voltage lead wire 143 from a power source 145 is connected to the photocathode 142. The power supply 145 is also connected to the active pixel sensor 147 via a lead wire 146. A vacuum chamber 148 separates the photocathode 142 from the active pixel sensor 147. Wall 150 represents the sealed outer wall of the chamber.

  The camera arrangement shown in the figure is intended to illustrate a useful system in connection with the present invention. The camera system should be easily optimized and can be modified as known in the prior art for specific applications. Thus, in a surveillance system, the captured image may include the inside or outside of the building area, where the camera lens is used to convert the image into a photocathode (in order, with a spatial shape, the image into an active pixel sensor). (Provide output cathode ray system or other display for viewing images in turn). As can be seen, the image 140 can be viewed on an integrated display or in a remote location in a system where the output of an active pixel sensor is provided. Such a screen can be arranged as shown at 154 as the output of the system.

  The type of camera shown can operate with a level of starlight-like light to image and reproduce the image, but typically and preferably operates in a bright environment (such as Should not be bright enough for people to pass at night). This is generally sufficient for most systems and conditions, and can therefore result in lower standards for the elements used in the system. For applications that require sufficient low-light imaging, such as for night vision purposes (helicopter flight where flight is very low and interested in accidents involving buildings, trees, or power lines) The system may be designed as shown, and may include unique means associated with night vision devices, such as battery operation, helmets, and the like.

  In scientific applications, it is necessary to operate in extremely dark situations. It is also necessary to handle the device without human damage. A system adjusted for night vision is almost useful for these purposes. In other scientific applications, it is required that a very low light emission can be imaged or even a single photon can be detected. The described system is also suitable for these applications.

  A related application is simultaneously filed by the inventor, Kenneth A. Costello, entitled Electron Bombarded Active Pixel Sensor Camera Incorporating Gain Control, and is referenced in connection with the present invention.

  Although the invention has been described with reference to particular embodiments, it will be apparent to those skilled in the art that various modifications can be made in the practice of the invention. Therefore, the present invention should be defined in accordance with the claims.

  FIG. 1 is a schematic diagram of the architecture of an active pixel sensor chip.   FIG. 2 is a schematic diagram of the architecture of a light-gated active pixel sensor.   FIG. 3 is a schematic diagram of a typical photodiode-type architecture of an active pixel sensor.   FIG. 4 is a schematic diagram illustrating an electron impact active pixel sensor of a vacuum tube apparatus according to the present invention.   FIG. 5 is a cross-sectional view of the photodiode pixel structure.   FIG. 6 is a schematic diagram of an active pixel sensor having an overlying light conversion layer.   FIG. 7 shows an image system or camera showing an application example of the present invention.

Claims (9)

A vacuum device,
A vacuum chamber (148),
A photocathode (31, 142) that forms part of the wall of the vacuum chamber and emits electrons into the vacuum chamber when receiving light;
An active pixel sensor (32, 147) including a semiconductor layer (57), located opposite the photocathode in the vacuum chamber;
A sidewall structure (39, 150) between the photocathode and the active pixel sensor and sealing the vacuum chamber;
An electronic connector extending from the active pixel sensor to the outside of the vacuum chamber for use outside the vacuum apparatus for signals from the active image sensor;
Including
An electric field is formed in the vacuum chamber to move electrons emitted from the photocathode into the vacuum chamber directly to the active pixel sensor;
The semiconductor layer (57) includes a photodiode or photogate pixel component for imaging using electron impact, and a CMOS circuit having transistors.
The active pixel sensor (32, 147) is disposed at a position where a rear surface of the active pixel sensor is impacted by electrons from the photocathode,
The vacuum device according to claim 1, wherein the active pixel sensor has a rear surface subjected to a passivated electron impact.
The semiconductor layer has a doping profile for forming a potential distribution in the semiconductor layer for deflecting the formed electrons away from the CMOS circuit and toward the photodiode or the photogate pixel structure. The vacuum apparatus according to claim 1, wherein the vacuum apparatus is characterized.
The vacuum apparatus according to claim 2, wherein a surface of the active pixel sensor is coated with an electro-optical conversion layer.
The vacuum apparatus according to claim 2, wherein a rear surface of the active pixel sensor is thinned, and electrons from the photocathode are directed to the thinned rear surface of the active pixel sensor.
Vacuum apparatus according to any one of claims 1 to 4, further low-light camera including a lens to focus the input image on the photocathode of the object plane.
The camera according to claim 5, wherein the active pixel sensor is coated with an electro-optical conversion layer, and the electro-optical conversion layer is positioned so that electrons emitted from the photocathode directly collide with the conversion layer. .
6. The camera of claim 5, wherein a rear surface of the active pixel sensor is thinned and electrons from the photocathode are directed to the thinned back layer of the active pixel sensor.
A method of recording a low light image,
Projecting an image to be recorded onto a photocathode and emitting electrons from the photocathode to a vacuum chamber with the spatial shape of the input image;
Placing an active pixel sensor including a semiconductor layer on a receiving surface of an electronic image in a vacuum chamber;
Directing the output of the active pixel sensor from the vacuum chamber to a recording device;
Including
An electric field for moving electrons emitted from the photocathode directly into the vacuum chamber to the active pixel sensor is formed in the vacuum chamber,
The semiconductor layer (57) includes a photodiode or photogate pixel component for imaging using electron impact, and a CMOS circuit having transistors.
The active pixel sensor (32, 147) is disposed at a position where a rear surface of the active pixel sensor is impacted by electrons from the photocathode,
The method of claim 1, wherein the active pixel sensor has a rear surface subjected to a passivated electron impact.
9. An active pixel sensor having an overcoating layer for converting an electronic image into a light image is positioned such that the electronic image from the photocathode is directed to the overcoating layer of the active pixel sensor. The method described.

Images